Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $29.57   9.446%   $32.3632   $32.36   $32.35   $32.40  
  Purchase #2 $224.30   4.264%   $233.8642   $233.86   $233.85   $233.90  
  Purchase #3 $161.58   5.664%   $170.7319   $170.73   $170.75   $170.70  
  Purchase #4 $216.34   11.625%   $241.4895   $241.49   $241.50   $241.50  
  Purchase #5 $172.77   5.721%   $182.6542   $182.65   $182.65   $182.70  
  Purchase #6 $93.61   4.247%   $97.5856   $97.59   $97.60   $97.60  
  Purchase #7 $34.38   8.520%   $37.3092   $37.31   $37.30   $37.30  
  7 purchase totals = $932.55       $995.9978   $995.99   $996.00   $996.10